The present invention relates to a cooling fan for use in a projector or the like apparatus incorporating a light source, wherein the cooling fan cools the inside of the apparatus while shielding (blocking) the inside light of the light source from shining through the fan.
The temperature inside a projector or the like apparatus incorporating a light source becomes high as a result of heat generation by the light source. In order to insure the safe operation, most of such apparatus are provided with a cooling fan in the cabinet, which fan cools the apparatus by circulating the ambient air in the cabinet.
In the first place, a commonly-used projector and a conventional cooling fan used in the projector are described with reference to FIG. 6 through FIG. 8. FIG. 6 is a cross-sectional view showing the outline of a conventional projector. FIG. 7 is a plan view of a conventional cooling fan for a projector. FIG. 8 shows a perspective view of an impeller of the conventional cooling fan.
Referring to FIG. 6, a projector 1 comprises a light source lamp unit 2, optical projection units 3 and 4, and a cooling fan 5. The cooling fan 5 is disposed behind the light source lamp unit 2, and a casing 6 is provided with exhaust holes 7 at a place corresponding to the cooling fan 5.
The cooling fan 5 has a housing 8 provided with an impeller opening 9. A motor (not shown) and an impeller 10 driven by the motor are disposed in the opening 9, as shown in FIG. 7. The impeller 10 is provided with a plurality of blades 11 protruding from an outer circumference of a boss portion 15. There are empty spaces (or gaps) 16 between the adjacent blades 11, as shown in FIGS. 7 and 8, which are provided for the purpose of easy separation of the impeller 10 from the dies after molding.
Not all of the light generated from the light source lamp unit 2 shines through the optical projection units 3 and 4 towards a screen (not shown). Rather, part of the light radiates to places other than the optical projection units 3 and 4. The light beams radiating to places other than the optical projection units 3 and 4 proceed through the gaps 16 between the blades 11 of the cooling fan 5, to eventually leak rearwardly out of the housing 8 through exhaust holes 7. This leaking of light beams rearwardly is annoying to persons viewing projected images who are sitting behind the projector 1. Effective measures for improving the above drawback have long been requested.
The gaps 16 between adjacent blades 11 of the impeller 10 could be narrowed, or even totally eliminated. But this would cause other difficulties related to manufacturing the impellers 10; namely, such impellers would be difficult to separate from the dies after molding, and would thus require an increased number of process steps.
Besides the above-described means for improvement, there have been other proposals. Namely, instead of providing the cooling fan 5 with a light shielding means, it has been proposed to provide a light shielding member in front, or behind, the cooling fan 5 (Japanese Patent No. JP 11167166A2 represents an example of such proposals). However, a light shielding member disposed in the front, or behind, the cooling fan 5 generally disadvantageously affects circulation of the air. This not only retards the cooling effect but it also tends to result in an increased number of parts in the apparatus, as well as increased assembly process steps.
The present invention addresses the above-described problems with the conventional cooling fans used in projectors or the like apparatus, and aims to offer such a cooling fan that has a light shielding property in itself, yet has an air handling capacity for circulating the cooling air that is not degraded. Furthermore, the constituent components of the fan, such as impeller, blades, etc., can be released easily from the dies after they are manufactured in a molding process.
A light shield fan of the present invention, which takes the air in at one end and exhausts it at the other end, comprises a housing, an impeller and a motor. The housing is provided with an impeller part having an opening for the impeller, and the impeller and the motor are disposed in the opening. The impeller comprises a plurality of blades provided along the outer circumference of a boss portion, and the blades appear overlapped with each other as viewed from the one end of the fan so that the incident light upon the one end of the fan is blocked thereby. The plurality of blades are radially extended from the boss portion of the impeller. Integration of these structures cancels the gaps formed between the sides of the blades, and light beams coming from the front are blocked by the blades.
In the light shield fan of the present invention, the plurality of blades on the circumference of the impeller is comprised of blades disposed at the intake side, or front stage blades, and blades disposed at the exhaust side, or rear stage blades. The front stage blades have an almost flat contour, while the rear stage blades are curved. There are gaps between the adjacent blades of the rear stage blades, and the gaps are overlapped by front stage blades so that the incident light coming from the one end of the fan is blocked. With the above-described structure, incident light from the front can be blocked at the impeller, while the fan""s air sending (or circulating) characteristic is not degraded. Thus the fan is ideal for use in projectors or the like apparatus incorporating a light source.
In a light shield fan in the present invention, the impeller is split into a front stage impeller having the front stage blades and a rear stage impeller having the rear stage blades. The front stage impeller and the rear stage impeller are integrated into a single component by a connecting member. With the above-described structure, the light coming from the front is blocked at the impeller, and the constituent components forming the impeller can be released easily from the dies after molding, while the air circulating characteristic of the fan is not degraded. Thus the fan is ideal for use in projectors or the like apparatus incorporating a light source.
In the light shield fan of the present invention, the inner diameter of the impeller opening in the housing is narrowed so that the inner diameter at the edge at the rear stage impeller side (i.e. at the rear edge) is smaller than that at the front stage impeller side (i.e. at the front edge). Narrowing of the opening""s inner diameter may be formed with either a sloped surface or a stepped shape. Furthermore, the inner diameter of the opening at the rear edge is at least 50% of that at the front edge. With the above-described structure, the light at the outer circumferential region of the blades can also be blocked. Thus the fan is ideal for use in projectors or the like apparatus incorporating a light source.